1. Field of the Invention
The present invention relates to dedicated power supply apparatuses, terminals, power supply systems, and power supply methods, and in particular, to a power supply technique applicable to mobile devices that can be carried around.
2. Description of the Related Art
A rapidly increasing number of mobile devices, such as digital audio players, that are small and can be carried around are being widely used. Many of these mobile devices are capable of performing high-speed data communication with computers by establishing universal serial bus (USB) connections. There are various methods for charging a battery in such a mobile device. For example, one method uses an alternating current (AC) jack for power supply, another method uses a cradle, and yet another method uses a USB. When a mobile device is provided with a USB terminal for data communication and an AC jack for power supply, the device becomes larger in size and is thus not attractive in appearance, and wiring connections become complicated. There are some mobile devices that are provided with cradles serving as dedicated chargers for holding and charging the mobile devices. Because it is necessary to have such large cradles at all times, it is difficult to make full use of the convenience of small mobile devices.
In view of the above-described points, it is preferable that USB-connectable mobile devices be charged by establishing USB connections. When charging is done by establishing USB connections, mobile devices can be charged by simply connecting them to computers. Therefore, many mobile devices that can be charged by establishing USB connections are not provided with an AC jack for power supply but are provided with only a USB jack for data communication and charging in order to reduce the size of the mobile devices, to not ruin the appearance of the mobile devices, and to enhance the simplicity of wiring connections.
In the case of mobile devices that are not provided with AC jacks for power supply, it is difficult to charge such a mobile device when there is no computer. In normal usage, such a mobile device is convenient since it can be charged by connecting it via USB to a computer. However, if a user of such a mobile device is on a trip and has no computer on hand, it is difficult to charge such a mobile device. In order to prevent this problem, adapters that can be connected to a home power supply, convert this power to predetermined power, and supply the predetermined power to mobile devices by establishing USB connections have been developed. Such adapters are referred to as “USB adapters” (for example, see Japanese Unexamined Patent Application Publication No. 2005-6497).